Conventionally, many video cameras and silver halide cameras have been marketed, which have built-in blur correcting functions for preventing an adverse effect on a sensed image caused by a blur such as a camera shake by a user during image sensing.
These blur correcting functions are roughly classified into a so-called electronic correction system and a so-called optical correction system. In the electronic correction system, that portion of an image sensed by an image-sensing device such as a CCD, which is to be displayed on a display, is changed in accordance with a camera shake, thereby displaying an image with no blur on the display. In the optical correction system, a sensor such as a vibration gyro senses a blur and, on the basis of the result of sensing, the apical angle of a variable apical angle prism is changed or a part of an image-sensing lens is shifted, thereby preventing a blur of a sensed image on an image-sensing surface.
These two systems will be briefly described below. In the electronic correction system, an output image signal from an image-sensing optical system is processed and temporarily stored in a field memory. An image signal of a present field output from the image-sensing optical system after that is compared with the image signal of the preceding field stored in the field memory. A blur amount of the present field is calculated from the preceding field, and the blur is corrected by shifting the image read position, as needed, so as to cancel the blur amount. This electronic correction system is primarily used to correct blurs of motion images obtained by video cameras and the like.
In the optical correction system, an image-sensing apparatus main body is equipped with an angular velocity sensor for sensing a blur. On the basis of an angular velocity signal obtained from this angular velocity sensor, the optical axis is shifted by an optical axis correction unit such as a variable prism placed in the optical path of an image-sensing optical system, thereby correcting the blur of an image on an image formation surface. This system does not deteriorate a sensed image by the correcting operation. Also, the angle of the optical axis is corrected in accordance with the angle of a shake of a camera main body. Hence, the influence of a camera shake can be well eliminated even when an image-sensing lens has a long focal length. This makes the system superior in image quality to the former system. This optical correction system is mainly used to correct blurs of still images obtained by silver halide cameras and the like.
Recently, so-called digital cameras which sense still images by an image-sensing device such as a CCD are finding widespread use in place of silver halide films. This digital camera is a new market field rapidly growing with the increasing needs for digital images by the spread of personal computers and with the improving image quality by the progress of technologies of various devices such as a CCD.
FIG. 8 is block diagram showing an outline of the arrangement of a conventional digital camera 101. An object image formed on an image-sensing device 103 by an image-sensing optical system 102 is converted into an image signal by the image-sensing device 103. This image signal is subjected to various processes by an A/D converter 104 and a signal processor 105 and saved in a recorder 106 such as a memory card. An image display 107 such as a monitor can display the image saved in the recorder 106 or an image currently being sensed by the image-sensing device 103. Of these components, the image-sensing optical system 102 has functions analogous to those of conventional silver halide cameras. The signal processor 105 and the display 107 have arrangements similar to video cameras.
Blur correction methods of the above image-sensing apparatus are classified into the electronic correction scheme and the optical correction scheme as described above, and these two schemes respectively have their drawbacks.
The electronic correction scheme is based on the condition that an image-sensing signal is obtained by an image-sensing device such as a CCD. Also, when blur correction is to be performed, enlarged reading (electronic zooming) is performed by omitting a peripheral portion of an entire image. Therefore, the corrected image is shifted to a telephoto side from the image-sensing field angle of the optical system, and the image quality deteriorates.
On the other hand, the optical correction scheme takes much time to activate the blur sensor such as a gyro sensor and also requires high power to drive these components.
Also, a digital camera as a kind of an image-sensing apparatus is required to display motion images on the monitor at any time, like a video camera, while an object image is observed, and to record still images with high image quality, like a silver halide camera, during image sensing.